English

The short exact sequence in definable Galois cohomology

Logic 2026-01-12 v3

Abstract

In Remarks on Galois Cohomology and Definability [2], Pillay introduced definable Galois cohomology, a model-theoretic generalization of Galois cohomology. Let MM be an atomic and strongly ω\omega-homogeneous structure over a set of parameters AA. Let BB be a normal extension of AA in MM. We show that a short exact sequence of automorphism groups 1Aut(M/B)Aut(M/A)Aut(B/A)11 \to \text{Aut}(M/B) \to \text{Aut}(M/A) \to \text{Aut}(B/A) \to 1 induces a short exact sequence in definable Galois cohomology. We also discuss compatibilities with [3]. Our result complements the long exact sequence in definable Galois cohomology developed in More on Galois cohomology, definability and differential algebraic groups [4].

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Cite

@article{arxiv.2408.04147,
  title  = {The short exact sequence in definable Galois cohomology},
  author = {David Meretzky},
  journal= {arXiv preprint arXiv:2408.04147},
  year   = {2026}
}

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17 pages